Feature/hee q16234

[gmlwjd9405]

No description provided.

[gmlwjd9405]

https://leetcode.com/problems/permutations/submissions/

// https://www.baeldung.com/java-array-permutations
public static List<List> result = new ArrayList<>();

public static void main(String ... args){
    permute(new int[]{1, 2, 3});
    System.out.println(result);
}

public static List<List<Integer>> permute(int[] nums) {
    recursive(nums.length, nums);
    return result;
}

public static void recursive(int n, int[] nums) {
    if (n == 1) {
        result.add(toList(nums));
        return;
    }

    for (int i = 0; i < n - 1; i++) {
        recursive(n - 1, nums);
        if (n % 2 == 0) { // 짝수
            swap(nums, i, n - 1);
        } else { // 홀수
            swap(nums, 0, n - 1);
        }
    }
    recursive(n - 1, nums);
}

public static void swap(int[] input, int a, int b) {
    int tmp = input[a];
    input[a] = input[b];
    input[b] = tmp;
}

public static List<Integer> toList(int[] input) {
    List<Integer> list = new ArrayList<>();
    for (int num : input) {
        list.add(num);
    }
    return list;
}